Phenyramidol (also known as Fenyramidol or IN 511 or MJ 505) is a drug chemically known as 2-(β-hydroxyphenethyiamino) pyridine of formula I, attributed for its analgesic and muscle relaxant properties.

The molecular formula for Phenyramidol is C13H14N20. Preparation of Phenyramidol was first described in 1959 in the Journal of the American Chemical society, indicated for the treatment of several types of pain.
Pain is often classified under various categories e.g. acute and chronic; nociceptive and neuropathic; pain accompanying inflammation (secondary to tissue injury); visceral (smooth muscle) pain and pain (body ache) associated with fever (temperature) etc.
Pain is defined by the International Association for the Study of Pain as an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage. Under normal circumstances pain is a result of the stimulation of peripheral receptors which transmit impulses to the brain through one or more pain pathways. Early treatment of pain is important as unrelieved pain can have profound psychological effects on the patient.
Opium is one of the most ancient pain relievers known to man. However both the habituation propensity and the addiction potential of opium are well known. The search for safe, effective and non habituating analgesics has been long lasting and continues even today, in the 21st Century. Many drugs pertaining to pure analgesics or analgesics with anti pyretic/anti inflammatory activity; analgesic and muscle relaxant activity etc have been invented with varying degrees of claims of superiority and safety. This range includes NSAIDS, COX-2 inhibitors, Aspirin, Codeine and its derivatives; Morphine and its derivatives, Caffeine and even Corticosteroids to relieve headaches; etc.
Serious side effects, including fatal episodes with COX-2 inhibitors have raised some serious thoughts in the medicinal research community regarding the development of New Chemical Entities (NCEs) for analgesic, anti-inflammatory, muscle relaxant and antipyretic therapeutic applications.
For the past few years, attention has been directed towards the search for new therapeutic indications for existing products and/or towards the examination of already existing old racemic molecules for their isomers of enhanced therapeutic activity.
Phenyramidol (2-{beta-hydroxyphenethylamino}pyridine) introduced originally as an analgesic has shown excellent skeletal muscle relaxant activity at very low doses when used parentally as well as orally. Phenyramidol is unique in its biological effects in that it possesses measurable analgesic and muscle relaxant properties. Of equal importance is the fact that other central effects observed with other analgesics or muscle relaxant drugs (such as sedation, euphoria, and mental confusion) have not been apparent in pharmacological studies of Phenyramidol. The analgesic activity of Phenyramidol is of the order of Codeine and its muscle relaxant activity can abolish abnormal muscle tone without impairing normal neuromuscular function.
The Phenyramidol molecule has an asymmetric carbon (chiral) centre and possesses optical activity. Presently this molecule is used as it is in the form of a ‘racemic’ mixture and to date no effort has been made to resolve its individual isomers and/or subject them to therapeutic evaluation for existing or new indications.
U.S. Pat. No. 4,168,308 discloses a composition for enhancing parenteral administration comprising a stable, oil-in-water emulsion containing a pharmacologically inert lipid as a hydrophobic phase dispersed in a hydrophilic phase and an effective dose of a pharmacologically active, oil-soluble agent predominantly dissolved in said lipid at a fraction ratio thereto in the hydrophobic phase. The oil-soluble pharmacological agent is a muscle relaxant such as Phenyramidol.
GB 1229967 discloses pharmaceutical compositions for enteral, parenteral and intranasal applications, comprising an oil-soluble therapeutic and/or diagnostic agent dispersed in a diluent comprising an emulsion or dispersion of a pharmaceutically inert lipid and water, at least 50% by weight of the active material being in the lipid phase. Numerous types of medicaments are mentioned and the examples relate to preparations comprising Phenyramidol, hexobarbital, hexyl ether, mecamylamine and quinidine.
Chiral chemistry of all kinds, from kinetic resolution to asymmetric synthesis, chiral chromatographic separation, racemisation and stereochemical inversion, to name a few—have formed the most dynamic subsection of the research activity involved in the development of new chemical entities. There is no relevant and/or useful prior art relating to the (R) and (S) isomers of Phenyramidol or the process for their resolution or for their chiral synthesis in the literature.
In spite of Phenyramidol being a 1959 molecule, no satisfactory chiral synthesis or characterization and therapeutic evaluation of optical enantiomers of Phenyramidol have been reported or attempted to date. There remains a need to accomplish the above objectives to achieve the improved pharmaco-therapeutic effects for patient benefit. Therefore the present inventors have met the long felt need in this invention.